In automotive finishing it is common to use a paint system composed of primer, surfacer, base coat and clear coat. Each of the various coats in the paint system has a number of special functions to take on.
The production of such multi-layer coatings, or of individual coats in such multi-layer coatings, has been described in numerous instances in the prior art.
The functions of the surfacer coat include levelling out unevennesses in the bodywork, ensuring effective adhesion to the primer and at the same time, by virtue of the coating's elastic properties, guaranteeing protection from sources of deep-down damage, such as that caused by stonechipping, for example. This surfacer is applied in two coats, with one coat intended to level out unevennesses in the bodywork and the second coat to produce the anti-stonechip properties. In the prior art, however, there have already been descriptions of aqueous surfacer systems which fulfil both requirements with a single surfacer coat.
The base coat, more particularly the metallic base coat, serves for producing good film-optical properties, high gloss levels and pronounced metallic effects of the coating system, and hence ensures an attractive appearance on the part of the painted article.
DE-A 195 42 626, DE-A 196 18 446 and DE-A 44 21 823 as well describe aqueous coating compositions comprising as component (I) a binder mixture composed of acrylate copolymer (A1) in organic solution and/or polyester resin (A2) and/or polyurethane resin (A3) and also as component (II) a non-blocked polyisocyanate crosslinker and as component (III) an aqueous dispersion of components (A1) and/or (A2) and/or (A3) and/or (A4). The systems described therein can be used as top coats, as surfacers or else as automotive refinish paints.
WO-A 98/12001 describes multi-layer coatings having improved anti-stonechip properties, composed of an aqueous base coat and of a special powder clear coat based on a polyacrylate resin capable of migration into the base coat. A disadvantage of this system is that the constituents of the base coat must be very highly compatible with the specific polyacrylates. The properties described therein are achieved only through the combination of an aqueous base coat with a special powder clear coat and through a specific curing method, with preliminary drying of the base coat at 90° C. and subsequent joint baking of base coat and powder clear coat.
There continues to be a need for suitable coating systems to make the painting operation more efficient and to enhance the level of properties of the multi-coat paint finishes.